Update genpdf docs

doc/source/code/genpdf.rst

@@ -3,40 +3,46 @@ genpdf
 
 We provide also a console script called ``genpdf`` that is able
 to generate and install a custom |PDF| set in the `lhapdf` format.
-In particular, the command ``genpdf install [NAME]`` simply
-install the |PDF| called ``[NAME]`` in the lhapdf folder and
-the ``genpdf generate [NAME]`` command generates the custom |PDF|
+
+To use it, you have to install the additional `ekobox` dependencies via
+the pip extra `box`:
+
+.. code-block:: bash
+
+  $ pip install eko[box]
+
+The ``genpdf generate [NAME]`` command generates a custom |PDF|
 and saves it as ``[NAME]`` in the current directory.
-Notice that the argument ``[NAME]`` is the only mandatory one.
+Afterwards, it can be conveniently installed using the ``genpdf install [NAME]`` command
+(which simply copies the generated folder into the LHAPDF folder)
+Note that the argument ``[NAME]`` is the only mandatory one.
 
-The custom |PDF| can be generated in three different ways which
-are accessible trough the option ``-p [PARENT]`` (the complete spelling
-is ``genpdf generate [NAME] -p [PARENT]``):
+A custom |PDF| can be generated in three different ways which
+are accessible trough the option ``-p [PARENT]``:
 
   1. If ``[PARENT]`` is the name of an available |PDF|, it is used as parent
-  |PDF| and thus copied to generate the new custom PDF.
-  2. If ``[PARENT]`` is "toylh" or "toy", the **toy** |PDF| is used as parent.
+     |PDF| and thus copied to generate the new custom PDF.
+  2. If ``[PARENT]`` is "toylh" or "toy", the **toy** |PDF| :cite:`Giele:2002hx,Dittmar:2005ed` is used as parent.
   3. If the option ``-p [PARENT]`` is not used, the |PDF| is
-  generated using **x(1-x)** for all the flavors.
+     generated using **x(1-x)** for all the flavors.
 
-Trough the use of the argument
-``[LABEL]`` (``genpdf generate [NAME] [LABEL] [OPTIONS]``) it is also possible
+Through the use of the argument
+``[LABEL]`` (``genpdf generate [NAME] [LABEL] [OPTIONS]``) it is possible
 to specify a set of flavors (expressed in |pid| basis) or a set of
-**evolution basis components** on which filtering the custom |PDF|.
-In this way the specified set is kept in the final |PDF|, while the rest
-is discarded.
+evolution basis components on which to filter the new |PDF|.
+In this way the specified set is kept in the new |PDF|, while the rest
+is discarded, i.e. set to zero.
 
 In the case of custom |PDF| generated starting from a parent |PDF|,
 it is possible to generate all the members trough the flag ``-m``. If this
 flag is not used, only the *zero* member is generated (together with the *info*
-file of course). Using the flag ``-m`` when the custom |PDF| is generated
-either using the **toy** |PDF| or the **x(1-x)** function, has no effects.
+file of course). Using the flag ``-m`` when a custom |PDF| is generated
+either using the **toy** |PDF| or the **x(1-x)** function has no effects.
 
 In order to automatically install the custom |PDF| in the lhapdf folder
 at generation time (so without using ``genpdf install [NAME]`` after the
 generation), it is possible to use the ``-i`` flag.
 
-
 We also provide an API with some additional features and possibilities
 such as generating a |PDF| with a custom function for every |pid|
 (through a ``dict`` structure) and filtering custom combination of
@@ -49,7 +55,7 @@ Examples
 
   $ genpdf generate gonly 21
 
-This will generate the custom PDF using the debug x(1-x) PDF as parent
+This will generate a custom PDF using the debug x(1-x) PDF as parent
 and then it will keep only the gluon.
 
 .. code-block:: bash
@@ -62,14 +68,22 @@ This will install the previous PDF in the lhapdf folder.
 
   $ genpdf generate Sonly S -p toy -i
 
-This will generate the custom PDF using the toy PDF as parent and then
+This will generate a custom PDF using the toy PDF as parent and then
 it will keep only the singlet combination. The generated PDF is also
 automatically installed in the lhapdf folder.
 
 .. code-block:: bash
 
   $ genpdf generate Vonly V -p CT10 -m
 
-This will generate the custom PDF using the CT10 PDF set as parent
+This will generate a custom PDF using the CT10 PDF set as parent
 (if available) and it will keep only the valence combination. Moreover
 it will generate all the members of the parent PDF.
+
+.. code-block:: bash
+
+  $ genpdf generate NN40qqbar -p NNPDF40_nnlo_as_01180 -- -5 -4 -3 -2 -1 1 2 3 4 5
+
+This will generate a custom PDF with no gluon contributions, but all quarks
+taken are from NNPDF4.0. Note that (as customary with CLIs) you have to add the explicit
+separator ``--`` before specifying anti-quark flavors.